Converting CAD Details to Revit Details:
Taken from Jay Zallan's Cad Vs. Bim Blog

Plan A - Redraw Details entirely in Revit
Plan B - Revitalize CAD Details you already have - Most used Plan

Revitalizing Details Explained (1 1/2 - 2 hour process typical)

First of all open the CAD detail and audit and purge it as well as verify that lines are not overlapping and that all joins are filleted.

• Begin new, blank "Detail Creation" project
• Create new Drafting View
• Name Drafting View after Detail
• Import CAD file into view (inverting colors and remember to set the import units to match the units in your CAD file)
• Explode (full) CAD file
  
  • You may be able to shave a little time off by using partial explodes depending on CAD file consistency
• Select all linework and change it from CAD's styles to one of Revit's linestyles.
  
  • You may change lineweights later in the final detail, but that's your call
• Convert in the same matter all CAD hatch patterns
• Convert in the same matter all CAD Text styles and recreate all leaders.
• Hide all Revit Text and Leaders
• Delete all exploded CAD Leaders and Arrow head remnants
• Unhide Revit Text and Leaders
• Verify that all geometry has been converted by selecting everything and hitting the "Filter" button.
  
  • If you only see Revit Items, then hit CTRL+C (Copy to Clipboard)
  • If you see any legacy CAD items or names, go back to the previous cleaning and converting steps until all are Revit geometry

The Paranoia Test

• Open another new, blank project
• Create a new Drafting View
• Name Drafting View after Detail to be Pasted
• CTRL+V (Paste from Clipboard)
• Select everything and hit the filter...
  • If it's all Revit Geometry, then detail is safe for project use
  • If it not, you will have to draw the geometry from scratch or spend lots of time troubleshooting CAD.

Plan C - Link predrawn CAD Details into separate Drafting Views